The present invention relates to a composite material member for a semiconductor device, and insulated and non-insulated semiconductor devices using the composite material member.
Conventionally, a material member that supports a semiconductor device substrate often serves also as one electrode for a non-insulated semiconductor device. In a power transistor device with power transistor chips mounted solidly on a copper base with a Pbxe2x80x94Sn solder material, the copper base (metal supporting member) serves both as a collector electrode of a transistor and a supporting member. This semiconductor device allows a few or more amperes of collector current to pass, causing the transistor chip to generate heat. In order to prevent instability of properties and reduction in lifetime caused by this heat-generation, the copper base also serves as a member for dissipation of heat. In addition, in the case where semiconductor chips with pressure resistance and adaptability to high-frequency enhanced so that a large amount of current can be passed therethough are directly mounted by soldering on a copper base, the role of the copper base is increasingly important not only as an intermediate member for dissipating heat but also for providing high reliability of the soldered mount.
In addition, in an insulated semiconductor device in which all the electrodes of the semiconductor device are insulated from metal supporting members, whereby the degree of freedom in circuit application of the semiconductor device can be increased, all the electrodes are insulated by insulating members from all package members including the metal supporting member and pulled to the outside. Therefore, even in a case example in which a pair of main electrodes is isolated from ground potential on the circuit, the package can be fixed to a ground potential portion irrespective of the electrode potential, thus making it easy to implement the semiconductor device.
Also, in an insulated semiconductor device, it is needed to dissipate efficiently heat generated during operation of the semiconductor device to outside of the package for operating the semiconductor element safely and stably. This dissipation of heat is usually achieved by transferring heat to the atmosphere from a semiconductor element substrate that is a source of generated heat through each member bonded thereto. The insulated semiconductor device includes in this heat transferring path an insulator, adhesive layers used in the portion to which the semiconductor substrate is bonded, or the like, and a metal supporting member.
In addition, the larger the amount of electric power needed by the circuit including the semiconductor device, or the higher the required reliability (stability with time, humidity resistance, heat resistance, etc.), the more complete insulation quality is required. The heat resistance mentioned herein includes heat resistance when a large amount of electric power is needed by the semiconductor device and thus the amount of heat generated in the semiconductor device is increased, in addition to heat resistance when the ambient temperature of the semiconductor device is increased due to an external cause.
On the other hand, the insulated semiconductor device generally has incorporated therein a certain integrated electric circuit including the semiconductor element substrate, and therefore it is necessary to electrically insulate at least part of the circuit from a supporting member. For example, in xe2x80x9cSemiconductor/DBS Substrate for Communicationxe2x80x9d: Electric Material (vol. 44, No. 5), p65-69 (1989) as a first prior art, is shown a power module device in which an assembly with Si chips mounted on an AlN ceramic substrate having copper plates bonded to the both faces (hereinafter referred to as copper-clad AlN substrate) is solidly attached to a copper supporting member by soldering with a solder.
In the above first prior art, the copper-clad AlN substrate has AlN-specific properties such as high thermal conductivity (190 W/mxc2x7K), low thermal expansibility (4.3 ppm/xc2x0 C.) and high insulation quality (1015 xcexa9xc2x7cm) in combination with copper-specific properties such as high thermal conductivity (403 W/mxc2x7K) and high electric conductivity (1.7xc3x9710xe2x88x926 xcexa9xc2x7cm), and is a component effective for mounting directly by soldering an electric power semiconductor element substrate (Si: 3.5 ppm/xc2x0 C.) in which current density is high and a significant amount of heat is generated to obtain a module device having excellent heat dissipation quality and reliability.
Generally, the copper-clad AlN substrate plays a role of insulating electrically from a copper supporting member a semiconductor element substrate mounted thereon by soldering or an electric circuit formed therein, and forming a heat flow pass from the semiconductor substrate to a cooling fin to enhance the dissipation effect thereof. In addition, with the copper-clad AlN substrate, a semiconductor substrate of small thermal expansivity can be mounted directly on the copper-clad AlN substrate without using a particular heat expansion control material (e.g. Mo and W), thus making it possible to reduce the number of components for the power module device and the number of integration processes.
In JP-A-8-111503 specification as a second prior art, there is disclosed a semiconductor current control device in which an assembly with Si chips mounted on a copper-clad AlN substrate is solidly attached by soldering with a solder to a supporting member composed of Mo. In this prior art, since the copper-clad AlN substrate is mounted by soldering on a Mo supporting member whose thermal expansivity (5.1 ppm/xc2x0 C.) is approximately same as that of the AlN substrate, the joint between these members is highly reliable, and works effectively for preventing degradation of heat dissipation quality.
In JP-B-7-26174 specification as a third prior art there is disclosed a semiconductor module device in which an assembly with thyristor chips mounted on an alumina substrate is mounted on a supporting member composed of a composite material with SiC ceramic powders dispersed on Al or an Al alloy (hereinafter referred to as Al/SiC composite material). In this prior art, since the alumina substrate is mounted on an Al/SiC composite material supporting member whose thermal expansivity (2.13 ppm/xc2x0 C.) is approximately same as that of the alumina substrate (7.5 ppm/xc2x0 C.), the joint between these members is highly reliable, and works effectively for preventing degradation of heat dissipation quality.
In JP-A-9-17908 specification as a fourth prior art there is disclosed a semiconductor device in which an assembly with Si chips mounted by soldering on a copper-clad AlN substrate is solidly attached by soldering with a solder to a supporting member composed of a composite material that is plane and has Cu layers (thermal conductivity: 403 W/mxc2x7K, thermal expansivity: 16.7 ppm/xc2x0 C.) and invar layers (Fe-36 wt % Ni, thermal conductivity: 15 W/mxc2x7K, thermal expansivity: 1.5 ppm/xc2x0 C.) alternately deposited in its main face in such a manner as to form a stripe pattern (hereinafter referred to as striped composite material). In this prior art, since the copper-clad AlN substrate is mounted by soldering with a solder on a striped composite material supporting member whose thermal expansivity (6.1 to 9.2 ppm/xc2x0 C.) is approximately same as that of the copper-clad AlN substrate, the soldered joint between these materials is highly reliable, and works effectively for preventing degradation of heat dissipation quality.
In xe2x80x9cClad Material CIC for Semiconductor Substratexe2x80x9d: Catalog of Hitachi Densen Co., Ltd. (CAT. No. B1-105), (April 1993) as a fifth prior art, is disclosed a heat sink material for power transistors for semiconductor substrates composed of a composite material with both faces of an invar layer cladded with Cu layers (hereinafter referred to as clad material, 4.0 to 10.6 ppm/xc2x0 C.). In this prior art, the clad material can be used as a member supporting a copper-clad AlN substrate with Si chips mounted thereon by soldering with a solder. Also in this case, since the thermal expansivity of the copper-clad AlN substrate is matched with that of the clad supporting member, the soldered joint between these materials is highly reliable, and works effectively for preventing degradation of heat dissipation quality.
On the other hand, even in the case of an insulated semiconductor device in which a ceramic insulating substrate like a copper-clad AlN substrate as described above is not used, an electric circuit including a semiconductor substrate is provided on the supporting member, and it is therefore necessary that this circuit be electrically insulated from the supporting member. For example, in xe2x80x9cMIST Substratexe2x80x9d by Akira Kazami: Industrial Material (vol. 30, No. 3), p.22-26 (1983) as a sixth prior art, is disclosed a substrate for hybrid integrated circuit device in which a copper foil (35 xcexcm) is formed, through an epoxy based insulation layer (28 xcexcm), on one face of an aluminum plate (1 to 2 mm) with alumite layers (14 to 30 xcexcm) formed on its both faces. In addition, a hybrid integrated circuit device is disclosed in which a power semiconductor element and a passive element are mounted by soldering with a solder on a substrate for hybrid integrated circuit device with the above described copper foil selectively etched to provide circuit wiring thereon.
In xe2x80x9cAn Improvement on Solder Joint Reliability for Aluminum Based IMST Substratexe2x80x9d by N. Sakamoto: IMC 1992 Proceedings, P. 525-532 (1992) as a seventh prior art, is disclosed a hybrid IC device in which a power transistor element and a ceramic condenser and chip resistors are mounted on the above substrate for hybrid integrated circuit device with a Pb-60 wt % Sn based solder, and these mounted elements are mold-sealed with an epoxy resin having thermal expansivity (25 ppm/xc2x0 C.) equivalent to that of aluminum.
The hybrid integrated circuit device and hybrid IC device based on the above described sixth and seventh prior arts may have a simple implemented structure because the semiconductor element substrate can be mounted directly on the substrate for hybrid integrated circuit device by soldering with a solder in the case where the amount of generated heat and the size of the semiconductor element substrate are not so large.
Generally, the semiconductor element substrate is bonded onto a mounting member with a solder of which melting point is relatively low. For example, in JP-A-4-49630 specification as an eighth prior art there is disclosed an Snxe2x80x94Sb based alloy solder, which is an alloy solder for assembly of semiconductor devices containing together Ni, Cu and P. In this case, it is said that the mechanical strength of the solder itself is enhanced by adding Sb to Sn to prevent an intermetallic compound of Nixe2x80x94Sn or Cuxe2x80x94Sn from being formed at the interface between a solder layer and the surface of a bonded member, thus making it possible to improve reliability of the semiconductor device.
In JP-B-3-3937 specification as a ninth prior art there is disclosed a semiconductor device in which a semiconductor element is attached to a mounting member supporting the element by soldering with a solder, in which the solder is composed of 87 to 92.4% by weight of tin, 7.0 to 10% by weight of antimony and 0.6 to 3.0% by weight of nickel. It is said that according to this technique, the mechanical strength of the solder is enhanced and formation of copper-tin alloys is curbed resulting in high reliability of the semiconductor device.
The insulated or non-insulated semiconductor device with the circuit element mounted thereon using the solder based on the above eighth and ninth prior arts may be a device serving approaches for preservation of environment in recent years, namely the purpose of establishing lead-free soldering.
An object of the present invention is to solve the above described problems and to provide a composite material member for a semiconductor device effective for obtaining a semiconductor device that alleviates thermal stress or thermal strain occurring during production or operation, has no possibilities of deformation, degeneration and rupture of each member, and is highly reliably and inexpensive, and insulated and non-insulated semiconductor devices using the composite material member.
In the case where the amount of heat generated in the semiconductor device is small and required reliability is not so high, any material may be used as a member constituting the device. In the case where the amount of generated heat is large and high reliability is required, however, the member to be applied should be selected.
Generally, in the insulated semiconductor device, a copper-clad AlN substrate with Si chips mounted thereon by soldering with a solder is solidly attached to a copper supporting member by soldering in a similar way as the first prior art. Here, the reason for using a copper plate of high thermal conductivity as a supporting member is that the plate is given a role in expanding the flow of heat transferred from the copper-clad AlN substrate to enhance the heat dissipation effect.
In this case, reduction in reliability based on destruction of the solder layer, cutoff of the heat pass, and destruction of the insulating substrate tends to occur due to large difference in thermal expansivity between the copper supporting member and copper-clad AlN substrate. Specifically:
(1) Because the thermal expansivity of the copper-clad AlN substrate is different from that of the copper supporting member, residual thermal stress and thermal strain are produced in the body into which the copper-clad AlN substrate and the copper supporting member are united. When the copper-clad AlN substrate is attached to the copper supporting member by soldering with a Pb-60 wt % Sn solder, they are subjected to thermal processing in which they are heated to a temperature above the melting point of the solder, and is then cooled down to room temperature. In this case, each member is shrunk in accordance with the thermal expansivity specific of each member with the members being fixed to each other at the freezing point of the solder, and thermal stress and thermal strain remains and deformation occurs in the bonded area. Generally, the electric power semiconductor substrate has a large size, and the power module device has the increased areas of the insulating substrate and the soldered portion because a plurality of semiconductor substrates and other elements are also mounted thereon. Therefore, the above described residual thermal stress and thermal strain are also significant, and deformation of the each member can be accelerated. The module device is repeatedly subjected to thermal stress during operation, and if the thermal stress is combined with the above described residual thermal stress or thermal strain, the heat pass will be cut off due to fatigue fracture of the solder layer, and the insulating substrate that is mechanically weak in nature will be damaged. Such events hinder normal operations of the module device, and damage of the insulating substrate in particular may cause a problem from the viewpoint of safety.
(2) Because thermal expansivity of the copper-clad AlN substrate is different from that of the copper supporting member, warping occurs in the body into which the copper-clad AlN substrate and the copper supporting member are united. If warping occurs in the module device, heat conducting grease cannot be loaded uniformly at the time when the device is attached to a cooling fin. As a result, thermal engagement between the copper supporting member and the cooling fin is not suitably made, and the heat dissipation quality of the route is degraded, thus making it difficult to conduct normal operation of the module device. In addition, in the case where the module device is mounted on the cooling fin by thread fastening, damage of the insulating substrate will be accelerated due to application of additional external stress.
The above described problems of (1) and (2) can be solved by selection of a supporting member with thermal expansivity matched with that of the copper-clad AlN substrate as in the case of the second to fifth prior arts. However, in the case where these supporting members are applied, new problems that are not found in the first prior art occur. That is, these problems are problems associated with preparation of members and incorporation of the supporting member into the semiconductor device, a problem associated with heat dissipation and a problem associated with costs. Specifically:
(a) Mo Supporting Member (Second Prior Art)
The Mo material is scarce metal, which is essentially expensive. In addition, the metal has a high melting point, and is so hard that it can hardly be processed mechanically. Thus, it is impossible to obtain a Mo ingot and to obtain a desired shape/size without significant disadvantage in terms of economy.
(b) Al/SiC Composite material Supporting member (Third Prior Art)
This supporting member has SiC powders dispersed in a matrix metal having Al as a main constituent by impregnating a porous preform consisting of SiC ceramic powders with liquid metal having mainly Al. In order to solder this member to the copper-clad AlN substrate, the surface of the Al/SiC composite material must be subjected to metalization processing that enables metallurgical engagement with the solder. In the case of a member of large size such as a supporting member of the power module device, however, a composite material that is flat and has high dimensional accuracy can hardly be obtained. Therefore, the composite material is subjected to metalization processing such as Ni plating after mechanical surface processing to obtain a desired shape and size. At this time, SiC particles as well as the Al area are exposed at the surface subjected to mechanical processing. The Ni plated layer is hardly precipitated at the surface of the SiC particle, or is not strongly bonded to the surface even if it is precipitated. This aspect can be pointed out as a problem associated with preparation of members.
Therefore, undesired phenomena such as peeling and blistering may occur at the interface between SiC and the Ni plated surface in the subsequent thermal process beginning with soldering. This aspect brings about an undesirable result in ensuring heat dissipation quality and reliability of the soldered joint in the semiconductor device. This aspect poses a problem associated with incorporation of components into the semiconductor device.
Thus, in addition to the fact that preparation of composite materials is difficult, the performance and yields of the resulting semiconductor device are adversely influenced, and therefore disadvantages in terms of economy cannot be negligible.
(c) Striped Composite Material Supporting Member (Fourth Prior Art)
This composite material can provide a relatively good heat dissipation effect in the sense that a striped Cu layer continuously extends from the copper-clad AlN substrate as an inlet of heat to the rear face of the supporting member as an outlet of heat. However, in order to obtain a desired shape and size, the composite material should be subjected to mechanical processing (e.g. rolling). At this time, there is a high possibility that a striped structure in which the Cu layer and the invar layer are alternately and regularly arranged loses its shape, and regularity in arrangement of the Cu layer and invar layer is lost, leading to a random pattern. This aspect poses a problem associated with preparation of members.
In addition, the properties of the striped composite material are varied depending on whether it is in the direction of stripe or in the vertical direction. In particular, variation in thermal expansivity may cause warping of the united body when the copper-clad AlN substrate is soldered with a solder. This warping extends even to the AlN substrate, resulting in breaking of the AlN substrate itself and degradation of insulation quality of the semiconductor device. In addition, when the semiconductor device is screwed into the cooling fin, further larger stress is produced. This also causes breaking of the AlN substrate and degradation of insulation quality. These aspects pose a problem associated with incorporation of components into the semiconductor device.
Thus, also in this case, in addition to the fact that preparation of composite materials is difficult, the performance and yields of the resulting semiconductor device are adversely influenced, resulting in disadvantages in terms of economy.
(d) Clad Material (Fifth Prior Art)
The clad material has Cu layers arranged on the both faces of the invar layer, and in order to keep this composite material flat, the Cu layers on the both faces must have the same thickness. However some imbalance in thickness could make it impossible to obtain a flat supporting member even if the imbalance is very small. This aspect poses a problem associated with preparation of members.
This defect may cause warping in the united body when the copper-clad AlN substrate is soldered, as in the case of the striped composite material. This leads to breaking of the AlN substrate, and in addition, breaking of the AlN substrate and degradation of insulation quality when the semiconductor device is screwed into the cooling body. These aspects pose a problem associated with incorporation of components into the semiconductor device.
In addition, for the clad material, the Cu layers on both sides are separated from each other by the central invar layer. The thermal conductivity of the invar layer is small (15 W/mxc2x7K), and therefore this layer acts so as to hinder transfer of heat flown from the copper-clad AlN substrate to the rear face of the supporting member. This aspect also poses a disadvantage associated with incorporation of components into the semiconductor device.
In the case of hybrid integrated circuit device and the hybrid IC device (hereinafter referred to as insulated semiconductor device) based on the sixth and seventh prior arts, a mounted component of small thermal expansivity, for example a semiconductor element substrate (3.5 ppm/xc2x0 C. (Si)) is fixed onto a circuit substrate of large thermal expansivity (Al: 23 ppm/xc2x0 C.) by soldering with a Pbxe2x80x94Sn based solder. The soldered portion plays a role to fix the mounted component in a predetermined position on the substrate and work as a wiring and heat dissipation pass in the semiconductor device. However, the above described semiconductor device is repeatedly subjected to thermal stress brought about at the time of operation and suspension, and ultimately the soldered portion suffers thermal fatigue rapture. In particular, if the thermal expansivity of resin is not appropriately adjusted for the substrate for hybrid integrated circuit when resin mold sealing is needed, excess residual stress will inherently exist in the interface between both members. If this stress is combined with the thermal stress at the time of operation of the semiconductor device, thermal fatigue rapture of the soldered portion is further accelerated. If the above thermal fatigue rapture continues, adverse effects will be brought about such as disconnection and cutoff of the heat dissipation pass. As a result, the semiconductor device will lose its circuit function. Thus, the first problem as to the semiconductor device based on the sixth and seventh prior arts is that means for alleviating excess stress based on a difference in thermal expansivity between the semiconductor element substrate and the circuit substrate is required.
In the case where the amount of heat generated in the semiconductor device is small and required reliability is not so high, the semiconductor substrate may be mounted on any circuit substrate. If a large amount of heat is generated and high reliability is required, the structure of the portion on which the semiconductor substrate is to be mounted should be appropriately selected. The circuit substrate based on the sixth and seventh prior arts has a sectional structure in which copper foil wiring is formed on an aluminum plate through an epoxy insulation layer. In the case where the semiconductor substrate as a heat source is mounted directly on the above circuit substrate by soldering, heat emitted from the semiconductor substrate is passed through a solder layer, copper foil wiring layer, epoxy insulation layer and aluminum plate in succession to the outside. The heat dissipation quality in the case of this mount structure is not so high. This is because the epoxy insulation layer of small thermal expansivity exists in the heat dissipation pass. If the heat dissipation quality is not sufficient, the temperature of the semiconductor substrate during operation is further increased to allow thermal runaway to occur, causing undesirable phenomena such as loss of circuit function as a semiconductor device, rupture of the semiconductor substrate itself, disconnection and short of the circuit, and degradation of insulation quality of the epoxy insulation layer. Thus, the second problem as to the device based on the sixth and seventh prior arts is that means for helping heat transfer in the heat dissipation pass between the semiconductor element substrate and the circuit substrate is required.
The composite material member for semiconductor device of the present invention to attain the above described objects is characterized by being a composite metal plate with particles composed of cuprous oxide dispersed in a copper matrix, wherein the surface of the composite metal plate is covered with a metal layer, and a copper layer with thickness of 0.5 xcexcm or larger exists in the interface formed by the composite metal plate and the metal layer.
The insulated semiconductor device of the present invention to attain the above described objects is characterized by being a semiconductor device with a semiconductor substrate mounted on a supporting member through an insulating member, or a semiconductor device with a semiconductor substrate mounted on a supporting member through an insulating member and an intermediate metal member in succession, wherein the semiconductor device comprises a composite material member in which at least one of the supporting member and the intermediate metal member is a composite metal plate with particles composed of cuprous oxide dispersed in a copper matrix, the surface of the composite metal plate is covered with a metal layer, and a copper layer with thickness of 0.5 xcexcm or larger exists in the interface formed by the composite metal plate and the metal layer.
The non-insulated semiconductor device of the present invention to attain the above described objects is characterized by being a semiconductor device with a semiconductor substrate mounted on a supporting member directly or through an intermediate metal member, wherein the semiconductor device comprises a composite material member in which at least one of the supporting member and the intermediate metal member is a composite metal plate with particles composed of cuprous oxide dispersed in a copper matrix, the surface of the composite metal plate is covered with a metal layer, and a copper layer with thickness of 0.5 xcexcm or larger exists in the interface formed by the composite metal plate and the metal layer.
The main feature in the composite material member for semiconductor device is that the surface of the composite metal plate with particles composed of cuprous oxide dispersed in a copper matrix is covered with a metal layer, and a copper layer with thickness of 0.5 xcexcm or larger exists in the interface formed by the composite metal plate and the metal layer. In addition, the main feature in the insulated semiconductor device or non-insulated semiconductor device is that at least one of the supporting member and the intermediate metal member comprises a composite material member in which the surface of a composite metal plate with particles composed of cuprous oxide dispersed in a copper matrix is covered with a metal layer, and a copper layer with thickness of 0.5 xcexcm or larger exists in the interface formed by the composite metal plate and the metal layer.
Based on the fact that such features are provided, an attempt is made to ensure strong connectivity, maintain dissipation quality and reliability and so on as to the insulated or non-insulated semiconductor device.
According to the present invention, a composite material member for semiconductor device effective for obtaining a semiconductor device that alleviates thermal stress or thermal strain occurring during production or operation, has no possibilities of deformation, degeneration and rupture of each member, and is highly reliably and inexpensive, and insulated and non-insulated semiconductor devices using the composite material member can be provided.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.